Although extensive safety measures and safe working procedures have been applied to improve and secure metal working machines, they still put their operators at risk. These risks might often result from manipulation errors, in particular if safety measures are ignored. In this contribution, a safety evaluation strategy has been developed that applies VR and mixed reality technologies to investigate the usability of working machines. An automatically controlled machine tool was simulated and connected to a real input panel, usually employed in industrial settings. However, Human-Machine Interfaces are sometimes built in a way that does not prevent the operator from cognitive misinterpretations which in turn might result in mistakes. To take that into account, a control program for a lathe was altered by hiding a typical programming mistake in the lines of code. Subjects were given the task to evaluate the program in single step mode and to report abnormalities while running the simulated lathe, comparable to new control program checks at real machines. An evaluation of the study demonstrated that even experienced metal workers accepted the simulation and reacted as if the given task was real. Behavioural data of considered subjects showed comparable profiles and most subjects rated the VR- based approach as a reasonable means for investigating work safety problems.